convert a suitable earth image from http://visibleearth.nasa.gov/view_rec.php?vev1id=11656 into .jpg and stick it in share/xplanet/images (I use the 170M 21600 x 10800 .tif , however you'll need a fast machine and more than 1G of ram to make this pleasant). To convert a .tif to a decent .jpg,

tifftopnm| pnmtojpeg

seems to work nicely.

download the markers file, and remove the header and footer. This sed will do the job: